Plastic deformation inhomogeneity in a single crystal nickel-base superalloy

Extension and compression tests at different temperatures with various strain rates have been carried out on DD8 single crystal superalloys with [0 0 1] [1 1 0] and [1 1 1] orientations. The results show that plastic deformation heterogeneity (P–L effect) occurs in the temperature range from 300 to 700 °C at the strain rate of 3.3×10−4 S−1 and also in the strain rate range of 1.3×10−4–5.3×10−4 S−1 at 700 °C for the [0 0 1]-oriented single crystal nickel-base superalloy during extension. The dependence of the plastic deformation inhomogeneity on the crystallographic orientations during compression under the strain rate of 1.0×10−4 S−1 at 550 °C were investigated, and the results indicate that the tendency to the plastic deformation inhomogeneity decreases in the order of [0 1 1], [0 0 1] and [1 1 1]. The mechanical tests display that this plastic instability may lead to the catastrophic drop in yield strength of the alloys, but can be removed by a new heat treatment, with which the yield strength can be improved.